Rotary actuator



July 5, 1966 M. c. SWANSON 3,258,980

ROTARY ACTUATOR Filed April 16, 1963 INVENTOR.

MILO C. SWflA/SON HIS flTTOENEYS United States. Patent 3,258,980 ROTARY ACTUATOR Milo C. Swanson, Cleveland, Ohio, assignor to Ledex, Inc., Dayton, Ohio, a corporation of Ohio Filed Apr. 16, 1963, Ser. No. 273,532 7 Claims. (CI. 7488) This invention relates to an improved rotary actuator and to a detent construction therefor, however, the invention is not necessarily so limited. This invention is an improvement upon the structure disclosed in copending application Serial No. 85,926, filed January 30, 1961 by Roger W. Biser, which is a continuation-in-part of Serial No. 606,711, filed August 28, 1956 (now abandoned), and results from efforts to miniaturize a device of the type disclosed in said applications.

In one of its forms, the device of the aforementioned applications is an electromagnetically energized actuator which produces a rotary stroke in an output shaft. The device involves a rotary conversion mechanism which is reset after each stroke of the output shaft and a spring is typically used to accomplish this reset operation. Also, for many applications, the device requires a detent mechanism for checking rotary motion of the output shaft during the reset operation and one or more springs are employed in the detent mechanism.

One of the problems involved in miniaturizing devices of this type resides in the design and location of the springs employed in the reset and detent mechanisms. Thus, for compactness, it is desirable to locate these springs interiorly of the operating parts, and, at the same time, for adequate tension and reliability of operation, it is essential to accommodate springs which are as large as possible.

Accordingly, it is an object of the present invention to provide a new and improved rotary actuator device having a novel construction and location for the spring elements associated therewith.

Another object of the present invention is to provide a new and improved mechanism for checking rotary movements.

Still another object of the present invention is to provide an improved rotary actuator construction including a detent mechanism for checking the rotary output and characterized by a compactness and reliability of operation.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

In the drawings, FIGURE 1 is a sectional view illustrating the interior construction of a rotary actuator device embodying the present invention.

FIGURE 2 is a sectional view, taken substantially along the line 22 of FIGURE 1.

FIGURE 3 is a sectional view, with a portion broken iijway, taken substantially along the line 33 of FIG- FIGURE 4 is a fragmentary, sectional view, taken substantially along the line 44 of FIGURE 3.

FIGURE 5 is a plan view, with a portion shown in section, illustrating a modified detent mechanism embodying features of the present invention.

Referring to the drawing in greater detail, the rotary actuator of FIGURE 1 includes a ferromagnetic element 12 having a cylindrical projection serving as a core 12a for an electromagnet. This core is surrounded by a solenoid coil 14, the interior periphery of which is insulated from the core by an insulating sheath 16. Electrical connection to the coil 14 is made through pins 18 supported in insulating inserts 19 mounted in the base of the element 12. For mounting of the rotary actuator, the element 12 may have a threaded bore 13 therein, as shown.

The element 12 has press-fitted thereon a hollow cylindrical housing 20 of ferromagnetic material which encloses the core 12a, the solenoid coil 14,- and the operative elements of the rotary actuator. Press-fitted in the housing 20 is an annular ring 22, this ring being positioned adjacent the outer or forward end of the solenoid coil 14. As best illustrated in FIGURE 2, this ring 22 has closely spaced axially extending flutes 24 in the inner periphery thereof, providing an irregular surface. As will be described more fully in the following, this fluted surface is util-ized in checking rotary movement in the actuator output.

An armature 26, responsive to the magnetic field of the electromagnet established in the core 12a by the coil 14, passes centrally through the annular ring 22. This armature supports an axially disposed output shaft 28 formed integrally thereon and projecting forwardly to the exterior of the housing 20. A circular plate 30, having a centrally disposed aperture 31 to receive the shaft 28, is press-fitted into the end of the housing 20, the plate 30 cooperating with the element 12 to substantially fully enclose the housing 20.

The armature 26 has an axially disposed bore 32 entering the rearward end thereof. A second radially disposed bore 34 passes diametrically through the armature 26 at the forward end of the bore 32. Disposed for axial movement in the bore 32 is a loosely fitting cylindrical piston or wedge member 36 having a frustum-conical forward end portion 42. The piston 36 is biased in a forward direction, that is, in the direction of the radially disposed bore 34, by means of a spring 38 acting against an abutment 40 having a stem 41 seated in a centrally disposed axially extending bore 43 formed in the core 12a.

The forward bias on the piston 36 is utilized to accomplish a detent or checking action in the following manner. Positioned in each of the opposite ends of the transverse bore 34 are two ball elements 46. The forward bias on the piston 36 forces the frustum-conical end 42 thereof against the innermost balls 46 disposed in the bore 34, thereby forcing these balls radially outwardly. This outward force is transmitted to the adjacent outer balls 46, which are thereby urged into the flutes of the ring 22. As best seen in FIGURE 2, the flutes 24 have a V-shaped cross section, so as to permit a rotation of the armature 26 provided the torque applied to the armature is suflicient to enable the sloping side walls of the flutes 24 to cam the balls 46 inwardly of the armature, overriding the outward bias applied by the spring 38. The axial extent of the flutes 24 is such as to permit limited axial movement of the armature without the ball elements 46 traveling axially out of the flutes.

The use of pairs of ball elements, as shown, for the detent action, offers a number of benefits. The outermost balls, of course, are free to roll on the inner periphery of the ring 22, as the armature rotates and, accordingly, a new surface is continually presented to the irregular inner surface of the ring 22. Thus, frictional wear, both in the ball elements and in the inner periphery of the ring 22 is minimized. At the same time, the rolling action of the outer ball elements 46 is transmitted to the inner ball elements, uniformly distributing the wear occasioned by contact of the inner ball element with the frustum-conical end portion of the piston 36. As further benefit, the ball elements 46 have a very small area of contact with the internal walls of the bore 34 and, accordingly introduce no appreciable frictional drag resisting the outward bias created by the spring 38.

It will be clear to those skilled in the art that the number of balls 46 to be used in accomplishing the foregoing detent action depends upon the dimensions of the rotary actuator unit. Thus, if the diameter of the actuator unit as disclosed is to be reduced substantially, one of the ball elements 46 may be eliminated from each end of the .bore 34. Similarly, if the dimensions are such that the diameter of the armature 26 may be increased, the number of ball elements 46 may be increased accordingly. It will also be apparent that without any significant change in the overall dimensions of the rotary actuator disclosed, the number of ball elements 46 employed may be reduced to two, one at each end of the bore 34, by substantially increasing the diameter of the bore to accommodate ball elements having a substan tially increased diameter. However, for optimum detent action, balls of comparatively small diameter are preferred and it is accordingly preferable to use a series of ball elements stacked one against the other, as shown.

For developing a rotary torque in the armature 26, an annular ferromagnetic plate or cam member 48 is press-fitted onto the forward end of the armature in surrounding relation to the output shaft 28. Interposed between the plate 48 and the forward wall surface of the ring 22 is a second annular plate or cam member 50, which is freely rotatable with respect to the armature 26. For reasons which will become more apparent in the following, the rearward surface of the plate 50 has bonded thereto a brake lining 52, adapted to frictionally engage the forward surface of the ring 22 when pressed thereagainst.

The opposing faces of the plates 48 and 50 are provided with arcuate inclined recesses 54 and 56 respectively, there being three recesses spaced 120 apart in each of the plate members 48 and 50. As best seen in FIGURE 4, the bases of these recesses are oppositely inclined and, as best seen in FIGURE 3, the side walls of the recesses diverge as the bases of the recesses penetrate more deeply into their respective plates.

Ball elements 60, there being three such ball elements, are interposed between opposing pairs of the recesses 54 and 56. The divergence of the side walls of the recesses is such as to permit these ball elements to roll into the deeper ends of the recesses. The arrangement of the recesses 54 and 56 is such that, with the interposed ball elements 60 disposed in the shallow ends of the recesses, an axially disposed force pressing the plates 48 and 58 toward one another, will cause the ball elements 60 to roll into the opposing recesses 54 and 56, at the same time, causing the plates 48 and 50 to rotate one relative to the other. For positioning the ball elements 60 in the shallow ends of the recesses 54 and 56, a crank arm 62 is fitted into an aperture in the plate 58 near the outer periphery of this plate. This crank arm 62 projects forwardly through an arcuate cut-out portion 64 in the plate 48. This cut-out portion 64 subtends an angle in the periphery of the plate 48 sufiicient to accommodate the full angle of rotation between the plates 48 and 50 produced by the ball elements 60 operating in their opposing recesses 54 and 56.

A second crank arm 66, best seen in FIGURE 3, also projecting in a forward direction, is press-fitted into a suitable aperture in the plate 48, this crank arm 66 being disposed adjacent the cut-out portion 64 in the plate 48, as shown in FIGURE 3. Engaging both of the crank arms 62 and 66 is a hairpin spring 68, which loops around the output shaft 28 and which has ends 70 curled about the crank arms 62 and 66. The tension in the spring draws the crank arms 62 and 66 toward one another and, when the actuator is idle, the spring occupies substantially the position illustrated in FIGURE 3. In such position, the ball elements 60 are seated in the shallow ends of the recesses 54 and 56, as illustrated in FIGURE 4.

The constru-ction is such that, upon energization of the solenoid coil 14, the element 12, housing 20, plate 48, and armature 26 form a flux path for the magnetic field created. The magnetic field attracts the armature toward the core 12a. This draws the plate 48 toward the plate 50 and, through the medium of the ball elements 60, the axial rearward thrust of the armature is transmitted to the plate 50 and applied to the ring 22 through the brake lining 52. This causes the plate 50 to frictionally engage the ring 22, so as to be temporarily non-rotatable relative to the housing 20.

The axial thrust of the armature 26 operating on the ball elements 60 causes these ball elements to roll into the opposing recesses 54 and 56, with the result that the plate 48 is caused to rotate relative to the plate 50. Since the plate is non-rotatable relative to the housing 20, the rotary motion occurs only in the plate 48, the armature 26 attached thereto and the output shaft 28 integral with the armature. Thus, as the armature 26 moves rearwardly, it is also induced to rotate.

As the armature 26 and, more specifically, the plate 48 rotates, the crank arm 66 is caused to move away from the crank arm =62, in opposition to the tension in the spring 68. The amount of rotation developed in this manner is determined by the lengh of the recesses 54 and 56 and, as previously mentioned, the angle subtended by the cut-out portion 64 and the plate 48 is sufficient to accommodate this rotation.

The rotary motion of the armature forces the ball elements 46 to move across one or more of the flutes 24 in the inner periphery of the ring 22. It is unimportant whether or not the ball elements 46 seat squarely in new flute-s 24 at the end of the rotary stroke.

When the solenoid coil 14 is deenergized and the magnetic field attracting the armature 26 has collapsed, the tension in the hairpin spring 68 induces a relative rotation between the plate 50 and the armature 26. Since the armature 26, together with its integral shaft 28 and any driven load attached thereto will ordinarily be considerably more massive than the plate 50, the rotary torque produced by the spring 68 will cause rotation primarily in the plate 50 with only a slight reaction in the armature 26. In the event the detent balls 46 are not squarely seated in flutes 24 at the end of the rotary stroke of the armature, the slight reaction in the armature, due to operation of the spring 68 coupled with the outward force on the ball elements 46 produced by the spring 38, causes the ball elements 46 to seat squarely in the closest available flutes 24 in the annular ring 22. Of course, once the ball elements 46 have seated squarely in flutes 24, all' of the rotary torque induced by the spring 68 is transmitted to the plate 50, with the result that the plate 50 is returned to its initial operating position, seating the ball elements 60 in the shallow ends of the opposing recesses 54 and 56.

As the plate 50 returns to its initial position, the ball elements 60 react in their respective recesses 54 and 56 to drive the plate 50 rearwardly relative to the armature toward the annular ring 22. This would ordinarily introduce a frictional drag opposing return of the plate 50.

In the present invention, this frictional drag is substantially eliminated by having the spring 38 act on the balls 46, which in turn act on the armature 26, so as to push the armature forward as the spring 68 acts to return the plate 50. This forward armature movement offsets the rearward movement of the plate 50 relative to the armature required for return of the plate 50 to its initial operating position. To insure this result, the spring 38 is made substantially stronger than the spring 68.

As can be noted in FIGURE 1, the armature has an annular shoulder 71 which engages the inner margin of the plate 50 as the armature returns forwardly under pressure of the spring 38. The shoulder 711 functions to provide a definite clearance between the plate 50 and annular ring 22 upon return of the armature to its initial position after deenergization of the electromagnet, thus removing frictional drag such as would resist manual rotation of the shaft 28 when the electromagnet is deenergized.

In the present construction, the forward motion of the armature 26 caused by pressure from the spring 38 is limited by an inwardly directed projection 33 on the end plate 30. An annular shoulder 74 on the armature 26 engages the spring 68 and drives this spring forwardly against a washer 72 buttressed by the projection 33. The dimensions of the projection 33 and washer 72 are such as to preclude a separation between the plate 50 and the annular ring 22 sufficient to permit escape of the ball elements 46 from the opposed pairs of recesses 54 and 56.

FIGURE 5 illustrates a modification of the detent assembly of FIGURE 1 and, furthermore, illustrates use of the detent mechanism in checking the rotary motion of a shaft 80. For housing the detent mechanism, the shaft 80 has integral radially disposed arms 82 through which passes a diametrically disposed boring 83. Oommunicating with the boring 83 is an axially disposed boring 84 entering one end of the shaft 80. Upon assembly of a piston 88 and biasing spring 90 inside the boring 84, this boring is closed with a plug 86 retained by a transverse pin 87.

Four ball elements are fitted in the boring 83, there being two on each side of the piston 88. The piston 88 has a frustum-conical forward end portion which, under the action of the spring 90, presses against the innermost ball elements 94 to urge the assembled balls outwardly of the arms 32. v

The shaft 80 is encircled by an annular ring 96 having axially disposed flute-s 98 disposed circumferentially around the inner periphery of the ring. The ring 96 may be supported by any suitable mounting, not illustrated.

The operation of the modification of FIGURE 5 is substantially the same as that of the preferred embodiment, in that the spring 90 acting against the piston 88 constantly urges the ball elements 94 against the inner periphery of the ring 96, the outermost ball elements seating in flutes 98 in the inner periphery of the ring 96 to check rotary movement of the shaft 80.

It will be noted that both the embodiments of FIG- URES 1 and 5 offer the advantage that the detent mechanism is assembled within the body to be checked, thus affording compactness to the apparatus in which the mechanism is employed. The essential difference between the embodiments of FIGURE 5 and FIGURE 1 is that in the embodiment of FIGURE 5, the spring 90 acts entirely Within the shaft 80, due to containment by the plug 86, whereas, in the embodiment of FIGURE 1, the spring 38 reacts against an abutment 40 which is supported independently of the armature 26. In the embodiment of FIGURE 1, the spring 3 8 is permitted to act against the abutment 40 to give the armature '26 a forward thrust, which is utilized to break a friction connec-' tion. It is to be recognized, however, that for other applications, such forward thrust may serve no useful purpose and in such cases, the detent assembly of FIG- URE S will sufiice.

In both the detent constructions illustrated, the detent balls 94 are confined within an annular ring and, accordingly, there is no necessity for caging the balls 46 or 94 in their boring. For some assemblies, however, it is recognized that caging of the balls 46 or 94 may be advantageous and, in such cases, it is within the purview of the present invention to employ any suitable means, such as an inwardly directed lip at the outer ends of the boring, for retaining the ball elements in the boring.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts,

the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. In an apparatus for producing rotary movement of a driven element, said apparatus comprising a housing receiving said driven element and in which said driven element has freedom for limited axial and rotary movement on a predetermined axis, said housing having a brake surface occupying a plane normal to said predetermined axis, motive means to deliver a rearward axial thrust to said driven element along said predetermined axis, and motion conversion means connected with said driven element responsive to said rearward thrust and engageable with said brake surface to cause rotation of said driven element relative to said housing, the improvement comprising resilient means coacting between said driven element and said housing to oppose said rearward axial thrust and operable upon relaxation of said rearward thrust to drive said driven element forwardly to release the frictional engagement between said motion conversion means and said brake surface.

2. In an apparatus for producing rotary movement of a driven element, said apparatus comprising a housing receiving said driven element and in which said driven element has freedom for limited axial and rotary movement on a predetermined axis, said housing having a brake surface occupying a plane normal to said predetermined axis, motive means to deliver a rearward axial thrust to said driven element along said predetermined axis, and motion conversion means connected with said driven element responsive to said rearward thrust and engageable with said brake surface to cause rotation of said driven element relative to said housing, the improvement comprising resilient means coacting between said driven element and said housing to oppose said rearward axial thrust and operable upon relaxation of said rearward thrust to drive said driven element forwardly to release the frictional engagement between said motion conversion means and said brake surface, said motion conversion means including a first cam member carried by said driven element, a second cam member spaced axially from said first cam member and adapted to frictionally engage said brake surface, means operating between said cam members to induce relative rotation thereof in one direction upon relative axial movement thereof one toward the other, and to induce relative axial movement thereof one away from the other upon relative rotation thereof in the opposite direction, and yielding means coacting between said cam members to oppose relative rotation thereof in said one direction, the construction;

and arrangement thereof being such that said second cam member is pressed against said brake surface upon rearward movement of said driven element whereby the relative rotation between said cam members in said one direction induced by such rearward movement results in rotation of said first cam member and said driven element relative to said housing, said yielding means acting upon relaxation of said axial thrust to reverse the induced relative rotation of said cam members and thereby cause relative axial movement of said cam members one away from the other, said resilient means driving said driven element forwardly upon relaxation of said rearward thrust to'offset the relative axial movement of said cam members caused by said yielding means, thereby releasing the frictional engagement between said second cam member and said brake surface.

3. In a rotary actuator assembly including a pair of opposing plate members, cam means operable between said plate members for inducing relative rotation thereof through a limited angle in one direction upon an application of pressure forcing said plate members one toward the other, first yielding means coacting between said plate members to oppose said rotary movement in said one direction and operable upon relaxation of said pressure to rotate said members relatively in the reverse direction, said cam means operating in response tov said reverse rotation to force said plate members one away from the other, a driven element, first connecting means to connect a first of said. plate members to said driven element, a supporting structure, second connecting means to connect the second of said plate members to said supporting structure, one of said first and second means including a brake surface positioned adjacent one of said plate members to form a brake therewith, and actuator means to apply a pressure to said plate members and said brake surface one through the other whereby said clutch is engaged atsubstantially the same time said plate members are forced one toward the other to induce relative rotation. thereof, the improvement comprising second yielding means effective to bias said brake surface and the other of said plate members apart, said second yielding means acting upon relaxation of the pressure from said actuator means to push said other plate member away from said brake surface offsetting the movement of said plate members one away from the other induced by said first yielding means and thereby releasing the brake engagement between said one plate member and said brake surface.

4. The rotary actuator assembly according to claim 3, wherein said relative rotation'between said plate members occurs about an axis passing normally through the opposingsurfaces of said plate members and wherein said cam means comprises-opposed arcuate inclined recesses in the opposing surfaces of said plate members concentric to said axis of relative rotation and a roller element interposed between said opposed recesses.

5. In a rotary actuator assembly, the improvement according to claim 3, wherein the other of said first and second connecting meansis a fixed connection and wherein said second yielding means is a compression spring operating between said supporting structure and said driven element, one of which carries said one plate and the other of which includes said brake surface.

6. In a rotary actuator assembly, the improvement according to claim 3, wherein the other of said first and second connecting means is a fixed connection and wherein said second yielding means is a compression spring operating between said supporting structure and said driven element, one of which carries said one plate and the other of which includes said brake surface, said driven element rotating relative to said supporting structure about an axis passing therethrough in response to pressure applied to said plate members and said brake surfaceby said actuator means, said supporting structure including an annular ring encircling said driven element concentricto said axis of rotation, said annular ring having an irregularly surfaced inner periphery opposite said driven element, said driven element having a first boring therein parallel to said axis receiving one end of said compression spring, said assembly including a piston disposed slidably in said first boring for engagement with said spring so as to receive an axial thrust therefrom, said driven element having a second boring therethrough transverse to and, intersecting with said first boring, said second boring being disposed in the plane of said annular ring and opening at each end thereof to the inner periphery of said annular ring, said piston having a wedge portion entering said second boring, and said assembly including detent means disposed in said second boring, there being one detent means in each end of said second boring and engaging opposite sides of said wedge portion, said compression spring acting on said piston to drive said detent means outwardly of the ends of said second boring against the irregularly surfaced inner periphery of said annular ring to thereby yieldingly check the rotation of said driven element.

7. Apparatus for inducing rotary movement of a driven element and checking the rotary movement thereof comprisingza housing receiving said driven element and in which said driven element has freedom for limited axial and rotary movement on a predetermined axis, said housing having a brake surface occupying a plane normal to said predetermined axis and spaced radially therefrom, motive means to deliver a rearward axial thrust to said driven element along said predetermined axis, motion conversion means responsive to said axial thrust to induce a simultaneous rotary movement of said driven element, said motion conversion means including a first cam member carried by said driven element and disposed in axially spaced relation to the brake surface of said housing, a second cam member interposed between said first cam member and said clutch surface, said second cam member having a rearward surface opposing the brake surface of said housing and adapted to engage in friction contact therewith, said second cam member having a forward surface opposing said first cam member, means coacting between said cam members to induce relative rotation thereof about said predetermined axis upon delivery of an axial thrust to said driven element, and yielding means opposing said relative rotation for resetting said cam members upon release of said axial thrust, said coacting means transmitting said axial thrust from said first cam member to said second cam member and thereby causing the forward surface of said second cam member to frictionally engage the surface of said housing whereby said driven element is induced to rotate relative to said housing, and check means to check the rotary movement of said driven element'for which said housing has an interior cylindrical and irregularly surfaced wall encircling said driven element concentric to said predetermined axis and said driven element has first and second communicating passages therein, said first passage traversing said driven element radially with respect to said predetermined axis and said second passage entering the rearward end of said driven element and extending forwardly of said driven element parallel to said predetermined axis to communicate. with said first passage, said check means comprising'a wedge member disposed for axial movement in said second passage and having-forwardly convergingexternal surfaces projecting into said first passage, a pair of detent means disposed in said first passage, there being one detent means on each side of said wedge member, each said detent means projecting radially from said wedge member to the exterior surface of said driven element, resilient means located in said second passage rearwardly of said wedge member, and abutment means secured fixedly to said housing for engaging said resilient means, said abutment means acting with said resilient means to bias said wedge member forwardly whereby said detent means are urged outwardly of said driven element through coaction of the converging surfaces of said wedge member to seat in irregularities of said cylindrical wall and thereby check 7 the rotary movement of said driven element, said resilient means acting uponrelaxation of such axial thrust to drive,

said driven element forwardly thus alleviating the frictional engagement between said brake surfaces.

References Cited by the Examiner UNITED STATES PATENTS BROUGHTON G. DURHAM, Primary Examiner. F. E. BAKER, Assistant Examiner. 

1. IN AN APPARATUS FOR PRODUCING ROTARY MOVEMENT OF A DRIVEN ELEMENT, SAID APPARATUS COMPRISING A HOUSING RECEIVING SAID DRIVEN ELEMENT AND IN WHICH SAID DRIVEN ELEMENT HAS FREEDOM FOR LIMITED AXIAL AND ROTARY MOVEMENT ON A PREDETERMINED AXIS, SAID HOUSING HAVING A BRAKE SURFACE OCCUPYING A PLANE NORMAL TO SAID PREDETERMINED AXIS, MOTIVE MEANS TO DELIVER A REARWARD AXIAL THRUST TO SAID DRIVEN ELEMENT ALONG SAID PREDETERMINED AXIS, AND MOTION CONVERSION MEANS CONNECTED WITH SAID DRIVEN ELEMENT RESPONSIVE TO SAID REARWARD THRUST AND ENGAGEABLE WITH SAID BRAKE SURFACE TO CAUSE ROTATION OF SAID DRIVEN ELEMENT RELATIVE TO SAID HOUSING, THE IMPROVEMENT COMPRISING RESILIENT MEANS COACTING BETWEEN SAID DRIVEN ELEMENT AND SAID HOUSING TO OPPOSE SAID REARWARD AXIAL THRUST AND OPERABLE UPON RELAXATION OF SAID REARWARD THURST TO DRIVE SAID DRIVEN ELEMENT FORWARDLY TO RELEASE THE FRICTIONAL ENGAGEMENT BETWEEN SAID MOTION CONVERSION MEANS AND SAID BRAKE SURFACE. 